1. Field of the Invention
The present invention relates to a vacuum gas releasing system, in particular a vacuum gas releasing system for removing bubbles in a high temperature molten matter, such as molten glass and metal, in a refining process for the high temperature molten matter.
2. Discussion of Background
As a vacuum degassing vessel, vacuum degassing vessels of siphon type, horizontal type, and so on are known. JP-A-3-33020 discloses an example that a vacuum degassing vessel of siphon type is applied.
In JP-A-3-33020, a vacuum degassing apparatus for molten glass mainly consisting of a melting tank, a rise tube, a vacuum degassing vessel, a down comer, and a storage tank. Molten glass, which has not been degassed, is stored in the melting tank, led from the riser tube to the vacuum degassing vessel, and degassed in the vacuum degassing vessel. The degassed molten glass is led from the down comer to the storage tank, and led to a forming process. This is a flow of the molten glass in the above vacuum degassing apparatus for molten glass.
Ordinarily, the vacuum degassing vessel is run under a depressurized state lower than the atmospheric pressure. Therefore, in the vacuum degassing vessel, a sealing mechanism for preventing air from leaking from the atmosphere to the vacuum degassing vessel is provided. However, because the above sealing mechanism can not sufficiently maintain a hermetical condition, leakage still occurs to a certain extent.
Therefore, a vacuum pump is connected to the conventional vacuum degassing vessel through a gas release pipe to suck air as much as a leaked quantity or more from the atmosphere by the vacuum pump for maintaining a degree of depressurizing in the vacuum degassing vessel.
Further, because it is difficult to stably maintain the degree of depressurizing using only the vacuum pump, an atmosphere leakage valve is connected to the vacuum degassing vessel to control an opening degree of the atmosphere leakage valve and the revolutional number of the vacuum pump, whereby the degree of depressurizing is stably maintained.
However, because in the conventional vacuum degassing vessel, the leakage valve is directly connected to the vacuum degassing vessel, there are the following problems. Namely, when the leakage valve is released, an outer air is introduced into the vacuum degassing vessel; a temperature in the vacuum degassing vessel is decreased; and the vacuum degassing vessel is unstably operated. Further, there is a problem that a gas releasing system is troubled and the vacuum degassing vessel is unstably operated because a large quantity of various volatile matters, such as water, SOX gas, carbon generated in the vacuum degassing vessel, are evacuated to the gas release pipe when an outer air passes through the vacuum degassing vessel.
Further, the volatile matters generated in the running vacuum degassing vessel intrudes into the gas release pipe along with a high temperature gas in a state of gas, liquid, and solid, even though the leakage valve connected to the vacuum degassing vessel is closed. Conventionally, there is a problem that the volatile matters chokes the gas release pipe, and resultantly the vacuum degassing vessel is unstably operated.